As is well known, an electrical switch is a device used to interrupt a flow of electrons (or current) in an electrical circuit. One type of switch includes two conductive pieces that are connected to an external circuit. The two conductive pieces (also referred to as contacts) can touch to complete (or make) the circuit, or the two conductive pieces can separate to open (or break) the circuit. In other words, when the contacts are touching, electricity can flow between them and the circuit is closed. When the contacts are separated, the switch is nonconducting (i.e., the circuit is open). A mechanism actuating a transition between these two states (i.e., open or closed) can be either a toggle (e.g., a flip switch for continuous “on” or “off”) or momentary (e.g., push-for “on” or push-for “off) type.
The mechanism of the electrical switch can be operated directly by an operator to control the electrical circuit (e.g., a light switch or a keyboard button). In other words, the switch can be directly manipulated by the operator as a control signal to a system, such as a computer keyboard button or to control power flow in a circuit, such as a light switch. Alternatively, the mechanism of the electrical switch can be operated by a sensing element for pressure, temperature, flow, etc. Non-limiting examples of switches include a proximity switch, speed switch, pressure switch, temperature switch, liquid level switch, liquid flow switch, etc.
In traditional temperature switches, a strip of two metals are joined together, wherein each metal has a distinct rate of thermal expansion. When the strip heats up or cools down, differing rates of thermal expansion between the two metals can cause the strip to bend. The bending of the strip can be used to actuate a switch mechanism to open or close an electrical switch. Other temperature switches can use a brass bulb filled with either a liquid or gas. As the bulb is heated, the gas or liquid expands, which generates a pressure increase. The increase in pressure can actuate the switch mechanism.
Traditional temperature switches generally involve discrete point measurements. For example, traditional temperature switches (or discrete point sensors) can be spread across an area in order to detect an over-temperature event (e.g., a fuel fire) in the area. However, the use of these traditional temperature switches often results in a compromise between probability of detection and the cost of a large number of switches. In other words, a likelihood of detecting the over-temperature event in the area increases when the number of switches in the area also increases. However, an increased number of switches can add weight, volume, complexity and cost.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.